AN ELECTRICALLY CONTROLLABLE COLLIMATOR IN A LASER RESONATOR

Description

Technical Field of the Invention

[0001] The invention provides a collimator for a laser assembly, such a laser assembly and a transmitter for an optical data network comprising such a laser assembly.

Background of the Invention

[0002] Tunable lasers are in high demand in optical communication systems because of their versatility. They are widely deployed in core networks but so far have been too expensive for use in access networks, i.e. in data transmission devices located at the customers' premises. Designs which are currently in use typically rely on sophisticated optoelectronic laser chips. An alternative is the extended cavity laser (ECL) which uses a low-cost gain chip combined with a mechanically tuned thin-film filter and a ball lens for collimation. The mechanically tunable laser design commonly offers three parameters with which the laser wavelength can be adjusted: the filter position (coarse-tuning of the laser gain profile), the laser current (fine-tuning of the cavity modes), and the laser temperature (fine-adjustment of the phase).

[0003] Using the laser temperature to fine-adjust the phase requires a costly Peltier cooler/heater and has the additional disadvantage of a slow response speed. As an alternative a cavity mirror may be moved by using a piezo-electric element which requires moving parts and therefore is expensive and not robust enough. Furthermore a semiconductor phase tuning section may be used, however, this needs optical pumping. Due to coupling losses between chips the gain and phase control section should be integrated on a single chip which requires sophisticated lithography which again is costly.

[0004] A document EP1906 214 A1 describes an electrowetting device. The device includes a conductive or polar liquid material, and an electrode applying to the liquid material through a dielectric layer. The device may be used for photographic lenses or optical recording. Embodiments of zoom lenses include two lenses arranged on a common axis.

[0005] Document WO 2004/1022251 A1 discloses an adjustable mirror including a first and a second fluid in contact over a meniscus extending transverse an optical axis. A meniscus adjuster is arranged to controllably alterat least one of the shape and position of the meniscus. The mirror may be adjusted to provide a desired mode in a laser arrangement.

Summary of the Invention

[0006] The invention as defined in claim 1 has been made in an effort to provide an inexpensive way of fine-adjusting the phase of a laser assembly that may overcome at least some of the above-mentioned disadvantages of the prior art.

[0007] A first aspect of the invention provides a collimator for a laser assembly including a first electrostatically controllable liquid lens having a first optical axis and a second electrostatically controllable liquid lens having a second optical axis aligned with the first optical axis. The collimator may be used instead of the ball lens used for collimating the laser mode. The focal lengths of the first and second electrostatically controllable liquid lenses may be adjusted synchronously in order to keep the focal length of the assembly constant while changing the optical path length of the cavity and therefore the phase matching condition.

[0008] As shown in Fig. 1, an electrostatically controlled liquid lens 10 may comprise a drop 11 of a hydrophobic liquid (e.g. silicon oil, 1-bromo-dodecane or similar substances) with an index of refraction n₂ attached to a specially prepared surface. The drop 11 may be immersed in a conducting liquid 12 such as an aqueous Na₂SO₄ solution with an index of refraction n₁. The drop 11 may be positioned on a surface area which may be treated to be hydrophobic and including a ring electrode 13. When a voltage is applied to the ring electrode 13, the drop 11 pulls away from the ring electrode 13 creating a steeper surface and decreasing the focal length of the liquid lens 10.

[0009] The invention includes the insight that an assembly of two liquid lenses may be controlled to have a constant focal length f while changing the focal lengths of each of the liquid lenses. However, since the form of the surface area of the drop 11 changes, so does the distance light travels through the drop of hydrophobic liquid having the index of refraction n₂. Since the optical path length is the product of the distance light travels in a medium and the index of refraction of the medium, the phase condition may be fine-tuned by controlling the shape of each of the liquid lenses while maintaining the focal length f of the collimator constant. Of course, the focal length f of the collimator may also be controlled which overcomes the need of precise mechanical fine-tuning of the laser assembly during the manufacturing process. However, once an optimum focal length f has been achieved, the focal length will be maintained constant while fine-adjusting the phase as described above.

[0010] Liquid lenses are designed for use in consumer application such a digital cameras or cameras used in mobile phones and therefore represent low-cost technology. Thus, the collimator according to the first aspect of the invention may be provided at low cost. In addition the collimator has an additional advantage in that the phase of a laser assembly may be fine-adjusted easily and rapidly because of the electric nature of the control signal and the high response speed of the liquid lenses. A further advantage of the collimator of the invention is that power consumption is low due to the electrostatic nature of the liquid lenses.

[0011] A second aspect of the invention provides a laser including a gain medium and a semitransparent mirror arranged at opposite sides of a laser cavity, a control circuit and a collimator according to the first aspect of the invention. Herein, the term "semitransparent" is not restricted to mirrors reflecting 50% of the incident light but rather describes the fact that the mirror reflects some of the incident light and transmits another part of the incident light. In laser technology semitransparent mirrors commonly reflect 80% or more of the incident light.

[0012] Preferably the collimator is arranged between the semitransparent mirror and the gain medium. In addition the laser may further include a dielectric filter arranged between the collimator and the semitransparent mirror.

[0013] The control circuit may have a first output connected to the first electrostatically controllable liquid lens and a second output connected to the second electrostatically controllable liquid lens. The control circuit may be adapted to provide a first control voltage for controlling the focal length of the first electrostatically controllable liquid lens to the first output and a second voltage for controlling the focal length of the second electrostatically controllable liquid lens to the second output, wherein a sum of the first voltage and the second voltage is set to a predetermined constant value.

[0014] A third aspect of the invention provides a transmitter for an optical data network comprising a laser according to the second inventive aspect.

[0015] The transmitter may further comprise an optical reference source adapted to provide an optical reference signal, an optical mixer adapted to mix the optical reference signal and an output signal of the laser and to thereby generate an intermediate frequency signal, and a local reference source adapted to provide a local reference frequency. The control circuit of the laser may be adapted to compare the intermediate frequency with the local reference frequency, preferably a quartz reference, and to control the collimator to increase the phase when the output frequency is higher than the local reference frequency and to decrease the phase when the output frequency is lower than the local reference frequency. In this way very stable control of the laser frequency is possible.

[0016] The control circuit of the transmitter may be adapted to determine an amplitude of the intermediate frequency signal. The control circuit may then be adapted to control the focal length of the collimator such that the amplitude of the output signal of the laser reaches a maximum. This approach may be implemented in all cases where the amplitude of the optical reference signal is constant or changing very slowly.

[0017] Alternatively, the transmitter may further comprise a monitor diode adapted to provide a feedback signal comprising an information about an amplitude of an output signal of the laser. Then, the control circuit may be adapted to control the focal length of the collimator such that the amplitude of the output signal of the laser reaches a maximum.

[0018] Numerous algorithms may be used for arriving at a maximum laser amplitude. E.g. a sweep through the different voltage settings for controlling the phase may be carried out measuring the amplitude for each voltage setting. Alternatively a search algorithm may be employed wherein the voltage is adjusted by a small step and the amplitude for the new voltage setting is compared to that for the previous voltage setting. If the amplitude has decreased, the direction of steps is reversed. Alternatively a low-frequency pilot tone may be used. Here, the focus is modulated continuously with a periodical signal, e.g. a sinus modulation. The control circuit may correlate the pilot tone with the measured amplitude and may derive the optimal focus control signal from that comparison.

[0019] The arrangement of lenses according to the invention allows to tune focus and phase independently. Nevertheless a modification of the focus may slightly affect the phase setting due to imperfections of the lenses and vice versa. To handle these interdependencies, the control block may apply different time constants to the filtering of the control signals for phase and focus. For example the time constant for phase control may be an order of magnitude smaller than that for focus control.

[0020] The algorithm for controlling focus may settle at a local extremum if multiple extrema exist in the amplitude. This problem can be circumvented by manual adjustment during manufacture which ensures that the algorithm starts near the optimum.

[0021] To avoid the manual adjustment an automatic adjustment routine may be carried out after rebooting or cold-starting the transmitter. During this routine the phase may be set to a fixed value and different focus settings may be tried. For each focus setting the laser current is modified, e.g. the laser current may be ramped up or down, while the amplitude of the laser is measured. From these measurements the threshold current of the laser for the given focus setting can be derived. Several focus settings are tested in this way, e.g. using a linear sweep over a range of focus settings, and the focus setting with the lowest threshold current will be selected for device operation.

[0022] If the transmitter is implemented in an optical data transmission device comprising a heterodyne receiver, the optical reference source may be the optical local oscillator of the receiver and the optical mixer may be the photo diode of the receiver.

Short Description of the Figures

[0023] The invention will be described more thoroughly referring to a plurality of figures which show:

Fig. 1

an electrostatically controllable liquid lens;

Fig. 2

a laser using a collimator according to the invention;

Fig. 3

a diagram illustrating the dependence of phase angle on the input voltage; and

Fig. 4

a transmitter comprising a laser according to the invention.

Detailed Description of the Figures

[0024] Fig. 2 shows a laser 20 using a collimator 23 according to the invention. A gain medium 21 and a semitransparent mirror 22 are located at opposite ends of a laser cavity. Since the gain medium 21 emits a mode having a finite angle, a collimator 23 is provided to collimate the light emitted by the gain medium 21. The focal length of the collimator 23 is chosen such that light reflected from the semitransparent mirror 22 is focussed at the same angle as the angle with which the gain medium 21 emits light. The laser 20 may further include a dielectric filter 24 which provides a coarse tuning mechanism which selects one of the cavity modes. The fine tuning of the modes is then done by phase adjustment.

[0025] Fig. 3 shows a diagram illustrating the dependence of phase angle on the input voltage of an exemplary liquid lens (e.g. the liquid lens 10 of Fig. 1) comprising a drop of 1-bromo-dodecane in an aqueous Na₂SO₄ solution. The optical power of a liquid lens 10 depends linearly on the voltage applied to the ring electrode 13. The optical power of the collimator of the invention can be described as this:

where f is the focal length of the collimator, f₁ and f₂ are the focal lengths of the first liquid lens and the second liquid lens, respectively, and

describes the relationship between the focal length f_i and the applied voltage V_i. α and β are constants which depend on the details of the assembly.

[0026] This construction has several advantages:

• - the tolerance for the distance of the lens assembly to the gain chip is greatly enhanced compared to the use of a fixed lens because the focal length can be adjusted after the assembly
• - adjusting the cavity phase requires no moving parts
• - because the optical power of each lens depends linearly on the applied voltage, all that needs to be done to keep the optical power of the assembly constant is to keep the sum of the applied voltages constant. This suggests the use of a simple control signal converter as controlling element (see Figure 4) wherein V₁=V+ΔV and V₂=V-ΔV.
• - the sensitivity of the device to voltage changes can be engineered by proper choice of the liquids; if the difference in refractive indices n₁ and n₂ is small, the same voltage change will result in a smaller phase change than if the difference is large.

[0027] The change in phase can be calculated as follows:

where Δz is the change in thickness of the entire lens assembly. For a spherical lens, which is a good approximation, the radius R of the sphere is related to the focal length f as

and therefore the change in phase can be reformulated:

[0028] Fig. 3 shows the resultant diagram for ΔΦ as a function of the input voltage V. The voltages in the example of Fig. 3 are comparatively high, however, power consumption remains low because the device is electrostatic. As already mentioned above, other materials may be chosen for the liquid lenses resulting in a higher difference between the indices of refraction n₁ and n₂ to arrive at lower control voltages.

[0029] Fig. 4 shows a laser arrangement 40 being part of a transmitter comprising a laser assembly 20 according to the invention. Those parts of the transmitter which are not required for understanding the invention have been omitted for ease of description. The laser 20 of the arrangement 40 is illustrated in Fig. 2 in detail. Accordingly, a detailed description of its components will be omitted at this place.

[0030] The laser arrangement comprises a control circuit 41 generating control signals for adjusting phase and focal length of the collimator 23 of the laser 20 (designated as Φ and f in Fig. 4). In Fig. 4 a separate control signal converter 45 is shown which may also form part of the control circuit 41. The control signal converter 45 converts the control signals for adjusting phase and focal length of the collimator 23 into control voltages suitable for the liquid lenses of the collimator 23.

[0031] In addition to the above, the control circuit 41 provides a laser current to the gain medium 21. The transmitter 40 further comprises an optical reference source 42 which provides an optical reference signal having a substantially constant wavelength or optical reference frequency. A part of the laser beam generated by the laser 20 and the optical reference signal are mixed in an optical mixer 43 thereby generating an intermediate signal having a frequency corresponding to a frequency difference between the optical reference signal and the frequency of the laser beam. For example a photo diode may be used as an optical mixer 43 yielding an electric signal which can be processed by the control circuit 41 easily. The control circuit 41 can control the phase of the laser 20 by comparing the intermediate frequency signal to a fixed reference signal such as a reference frequency provided by a quartz oscillator and adjusting the phase accordingly. In this way the phase of the laser 20 and thus the frequency of the laser 20 are controlled to always correspond to the frequency of the optical reference source minus the frequency of a fixed reference signal similarly to a Phased-locked Loop (PLL).

[0032] The exemplary transmitter 40 shown in Fig. 4 further comprises a monitor diode 44 which is adapted to generate a signal comprising an information about an amplitude of the laser beam generated by the laser 20 and provide this signal to the control circuit 41. The process of adjusting phase and frequency of the laser carried out by the control circuit 41 has been described above in detail.

References

[0033] 

10

liquid lens

11

drop

12

conducting liquid

13

ring electrode

20

laser assembly

21

gain medium

22

semitransparent mirror

23

collimator

24

dielectric filter

40

laser arrangement

41

control circuit

42

optical reference source

43

optical mixer

44

monitor diode

45

control signal converter

R

radius

f

focal length

n₁, n₂

refractive indices

ΔΦ

phase

Claims

1. A collimator (23) for a laser assembly (20) including a first electrostatically controllable liquid lens (10) having a first optical axis and a second electrostatically controllable liquid lens (14) having an aligned second optical axis,
wherein
each lens (10, 14) is independently controllable;
the liquid lenses (10, 14) are arranged close together forming a ball lens and
the ball lens (10, 14) contains liquids with different refractive indices (n1, n2).

2. The collimator (23) of claim 1, further adapted to maintain a focal length (f) of the collimator (23) constant while changing an optical path length of the collimator (23) according to first and second control voltages (V₁; V₂) received by the first and second electrostatically controllable half ball lenses (10, 14) according to


wherein V₁ = V + ΔV, V₂ = V - ΔV.

3. The collimator (23) of one of the claims 1 - 3, wherein

- the first electrostatically controllable half ball lens (10) and the second electrostatically controllable second half ball lens (14) each comprise a drop (11) of a hydrophobic liquid, preferably of silicon oil or 1-bromo-dodecane, having a first refractive index (n₁) immersed in a conducting liquid (12), preferably an aqueous Na₂SO₄ solution, having a second refractive index (n₂) different from the first refractive index (n₁); and

- each ring electrode (13) adapted to apply an electric field to each drop (11) of each hydrophobic liquid.

4. A laser arrangement including a gain medium (21) and a semitransparent mirror (22) arranged at opposite sides of the , gain medium (21), and a control circuit (41), characterised by a collimator (23) according to one of the preceding claims arranged between the semitransparent mirror (22) and the gain medium (21).

5. The laser arrangement of claim 4, further including a dielectric filter (24) arranged between the collimator (23) and the semitransparent mirror (22).

6. A laser arrangement (40) including a laser (29) according to claim 4 or 5, further comprising

- the control circuit (41) and a control signal converter (45) connected downstream in series with a first output connected to the first electrostatically controllable liquid half ball lens (10) and a second output connected to the second electrostatically controllable liquid half ball lens (14), the control circuit (41) and the control signal converter (45) being adapted to provide a first control voltage (V1) for controlling the focal length f1 of the first electrostatically controllable liquid half ball lens (10) and a second voltage (V2) for controlling the focal length f2 of the second electrostatically controllable liquid half ball lens (14), wherein a sum of the first control voltage and the second control voltage (V1 + V2) is set to a predetermined constant value determining the overall focal length (f) and the difference of the control voltages (V1 - V2) determines a optical path length of the collimator / phase difference (ΔΦ).

7. The laser arrangement (40) according to claim 8, wherein

- the control circuit (41) outputs a first control signal determining the focal length (f) of the collimator (23) and a second control signal (ΔU) determining the optical path length / phase of the collimator, and wherein

- the control signal converter (45) converts the control signals (U, ΔU) into the first control voltage (V1) and the second control voltage (V2).

8. A laser arrangement (40) for an optical data network according to one of the claims 4 - 7, further comprising

- an optical reference source (42) adapted to provide an optical reference signal, an optical mixer (43) adapted to mix the optical reference signal and an output signal of the laser (20) and to thereby generate an intermediate frequency signal, and a local reference source adapted to provide a local reference frequency, wherein the control circuit (41) of the laser (20) is adapted to compare the intermediate frequency with the local reference frequency, preferably a quartz reference, and to control the collimator (23) to increase the phase when the output frequency is higher than the local reference frequency and to decrease the phase when the output frequency is lower than the local reference frequency.

9. The laser arrangement (40) of claim 8, wherein the control circuit (41) is adapted to determine an amplitude of the intermediate frequency signal and to control the focal length of the collimator (23) such that the amplitude of the output signal of the laser (20) reaches a maximum.

10. The laser arrangement (40) of one of the claims 8 or 9, further comprising
a monitor diode (44) adapted to provide a feedback signal comprising an information about an amplitude of an output signal of the laser (20), wherein the control circuit (41) is adapted to control the focal length of the collimator (23) such that the amplitude of the output signal of the laser (20) reaches a maximum.

11. An optical data transmission device, comprising

- a heterodyne receiver and a laser arrangement (40) according to one of the claims 4 - 10, wherein the optical reference source (42) is an input signal of the heterodyne receiver.

12. An optical data transmission device comprising

- a heterodyne receiver and a laser arrangement (40) according to claim 8 - 10, wherein the optical mixer (43) is a photo diode for receiving an optical data signal of the heterodyne receiver.

Ansprüche

1. Kollimator (23) für einen Laseraufbau (20), umfassend

eine erste elektrostatisch steuerbare Flüssigkeitslinse (10) mit einer ersten optischen Achse und

eine zweite elektrostatisch steuerbare Flüssigkeitslinse (14) mit einer ausgerichteten zweiten optischen Achse,

wobei
die Linsen (10, 14) unabhängig voneinander steuerbar sind;
die Flüssigkeitslinsen (10, 14) nahe beieinander angeordnet sind und eine Kugellinse bilden, wobei die Kugellinse (10, 14) Flüssigkeiten mit unterschiedlichen Brechungsindizes (n₁, n₂) enthält.

2. Kollimator (23) nach Anspruch 1, der dazu eingerichtet ist, eine Brennweite (f) des Kollimators (23) während einer Änderung einer optischen Weglänge des Kollimators (23) gemäß


konstant zu halten,
wobei die optische Weglänge des Kollimators (23) gemäß einer ersten und einer zweiten Steuerspannung (V₁;V₂), die jeweils von der ersten bzw. der zweiten elektrostatisch steuerbaren halben Kugellinse (10, 14) empfangen werden, geändert wird, und
wobei

3. Kollimator (23), nach Anspruch 1 oder 2, wobei
die erste elektrostatisch steuerbare halbe Kugellinse (10) und die zweite elektrostatisch steuerbare halbe Kugellinse (14) jeweils einen Tropfen (11) einer hydrophoben Flüssigkeit, vorzugsweise von Silizium-Öl oder von 1-Bromdodecan, mit einem ersten Brechungsindex (n₁) umfassen, wobei die Tropfen (11) jeweils von einer leitfähigen Flüssigkeit (12), vorzugsweise einer wässrigen Na₂SO₄-Lösung, umgeben sind, wobei die leitfähige Flüssigkeit (12) einen zweiten Brechungsindex (n₂) aufweist, der sich von dem ersten Brechungsindex (n₁) unterscheidet; und
jede Ringelektrode (13) dazu eingerichtet ist, an die jeweiligen Tropfen (11) jeder der hydrophoben Flüssigkeiten ein elektrisches Feld anzulegen.

4. Laseranordnung mit einem Gain-Medium (21) und mit einem teilweise transparenten Spiegel (22), der auf einer gegenüberliegenden Seite des Gain-Mediums (21) angeordnet ist, und mit einer Steuerschaltung (41), gekennzeichnet durch einen Kollimator (23) nach einem der vorhergehenden Ansprüche, der zwischen dem teilweise transparenten Spiegel (22) und dem Gain-Medium (21) angeordnet ist.

5. Laseranordnung nach Anspruch 4, die weiterhin einen dielektrischen Filter (24) umfasst, der zwischen dem Kollimator (23) und dem teilweise transparenten Spiegel (22) angeordnet ist.

6. Laseranordnung (40) mit einem Laser (20) nach Anspruch 4 oder 5, die weiterhin Folgendes umfasst:

die Steuerschaltung (41) und

einen ausgangsseitig in Serie verbunden Steuersignalwandler (45), der mit einem ersten Ausgang mit der ersten elektrostatisch steuerbaren halben Flüssigkeits-Kugellinse (10) verbunden ist und der mit einem zweiten Ausgang mit der zweiten elektrostatisch steuerbaren halben Flüssigkeits-Kugellinse (14) verbunden ist,

wobei die Steuerschaltung (41) und der Steuersignalwandler (45) dazu eingerichtet sind,

eine erste Steuerspannung (V₁) zum Steuern der Brennweite f₁ der ersten elektrostatisch steuerbaren halben Flüssigkeits-Kugellinse (10) bereitzustellen und

eine zweite Spannung (V₂) zum Steuern der Brennweite f₂ der zweiten elektrostatisch steuerbaren halben Flüssigkeits-Kugellinse (14) bereitzustellen,

wobei die Summe der ersten Steuerspannung und der zweiten Steuerspannung (V₁ + V₂) auf einen vorbestimmten konstanten Wert, der die Gesamtbrennweite (f) bestimmt, eingestellt ist und
wobei der Unterschied der Steuerspannungen (V₁ - V₂) eine optische Weglänge des Kollimators / einen Phasenunterschied (ΔΦ) bestimmt.

7. Laseranordnung (40) nach Anspruch 6, bei der

- die Steuerschaltung (41) ein erstes Steuersignal ausgibt, das die Brennweite (f) des Kollimators (23) bestimmt, und ein zweites Steuersignal (ΔU) ausgibt, das die optische Weglänge / die Phase des Kollimators bestimmt, und bei der

- der Steuersignalwandler (45) das Steuersignal (U, ΔU) in die erste Steuerspannung (V₁) und in die zweite Steuerspannung (V₂) umwandelt.

8. Laseranordnung (40) für ein optisches Datennetzwerk nach einem der Ansprüche 4 bis 7, die weiterhin Folgendes umfasst:

- eine optische Referenzquelle (42), die dazu eingerichtet ist, ein optisches Referenzsignal bereitzustellen,

- einen optischen Mischer (43), der dazu eingerichtet ist, das optische Referenzsignal mit einem Ausgangssignal des Lasers (20) zu mischen, um ein Zwischenfrequenzsignal zu erzeugen, und

- eine lokale Referenzquelle, die dazu eingerichtet ist, eine lokale Referenzfrequenz bereitzustellen, wobei die Steuerschaltung (41) des Lasers (20) dazu eingerichtet ist,
die Zwischenfrequenz mit der lokalen Referenzfrequenz, vorzugsweise einer Quarzreferenz, zu vergleichen und
den Kollimator (23) zu steuern, um die Phase zu vergrößern, wenn die Ausgangsfrequenz größer als die lokale Referenzfrequenz ist, und um die Phase zu verkleinern, wenn die Ausgangsfrequenz kleiner als die lokale Referenzfrequenz ist.

9. Laseranordnung (40) nach Anspruch 8, bei der die Steuerschaltung (41) dazu eingerichtet ist, eine Amplitude des Zwischenfrequenzsignals zu bestimmen und die Brennweite des Kollimators (23) zu steuern, sodass die Amplitude des Ausgangssignals des Lasers (20) ein Maximum erreicht.

10. Laseranordnung (40) nach Anspruch 8 oder 9, die weiterhin eine Monitordiode (44) umfasst, die dazu eingerichtet ist, ein Feedbacksignal bereitzustellen, das eine Information über eine Amplitude eines Ausgangssignals des Lasers (20) umfasst, wobei die Steuerschaltung (41) dazu eingerichtet ist, die Brennweite des Kollimators (23) zu steuern, sodass die Amplitude des Ausgangssignals des Lasers (20) ein Maximum erreicht.

11. Optische Datenübertragungsvorrichtung, die einen heterodynen Empfänger und eine Laseranordnung (40) nach einem der Ansprüche 4 bis 10 umfasst, wobei die optische Referenzquelle (42) ein Eingangssignal des heterodynen Empfängers ist.

12. Optische Datenübertragungsvorrichtung, die einen heterodynen Empfänger und eine Laseranordnung (40) nach einem der Ansprüche 8 bis 10 umfasst, bei der der optische Mischer (43) eine Fotodiode zum Empfangen eines optischen Datensignals des heterodynen Empfängers ist.

Revendications

1. Collimateur (23) pour ensemble laser (20) comprenant une première lentille liquide contrôlable électrostatiquement (10) ayant un premier axe optique et une seconde lentille liquide contrôlable électrostatiquement (14) ayant un second axe optique aligné,
où
chaque lentille (10, 14) est contrôlable de manière indépendante ; les lentilles liquides (10, 14) sont disposées à proximité l'une de l'autre pour former une lentille sphérique et la lentille sphérique (10, 14) contient des liquides ayant des indices de réfraction différents (n₁, n₂).

2. Collimateur (23) selon la revendication 1, en outre conçu pour maintenir constante une longueur focale (f) du collimateur (23) tout en changeant une longueur de chemin optique du collimateur (23) suivant des première et seconde tensions de commande (V₁; V₂) reçues par les première et seconde lentilles demi-sphériques contrôlables électrostatiquement (10, 14) suivant la relation 1/f = 1/f₁ + 1/f₂ = αV₁ + αV₂ + 2β = constante,

3. Collimateur (23) selon une des revendications 1 à 3, dans lequel la première lentille demi-sphérique contrôlable électrostatiquement (10) et la seconde lentille demi-sphérique contrôlable électrostatiquement (14) comprennent chacune une goutte (11) de liquide hydrophobe, de préférence de l'huile de silicone ou du 1-bromo-dodécane, ayant un premier indice de réfraction (n₁) et immergé dans un liquide conducteur (12), de préférence une solution aqueuse de Na₂SO₄ ayant un second indice de réfraction (n₂) différent du premier indice de réfraction (n₁) ; et
chaque électrode annulaire (13) étant conçue pour appliquer un champ électrique à chaque goutte (11) de chaque liquide hydrophobe.

4. Ensemble laser comprenant un milieu de gain (21) et un miroir semi-transparent (22) disposés à des côtés opposés du milieu de gain (21), et un circuit de commande (41), caractérisé par un collimateur (23) conformément à une des revendications précédentes disposé entre le miroir semi-transparent (22) et le milieu de gain (21).

5. Ensemble laser selon la revendication 4, comprenant en outre un filtre diélectrique (24) disposé entre le collimateur (23) et le miroir semi-transparent (22).

6. Ensemble laser (40) comprenant un laser (29) selon la revendication 4 ou la revendication 5, comprenant en outre :

le circuit de commande (41) et un convertisseur de signal de commande (45) connecté en aval en série avec une première sortie connectée à la première lentille demi-sphérique à liquide contrôlable électrostatiquement (10) et une seconde sortie connectée à la seconde lentille demi-sphérique à liquide contrôlable électrostatiquement (14), le circuit de commande (41) et le convertisseur de signal de commande (45) étant conçus pour délivrer une première tension de commande (V₁) pour contrôler la longueur focale f₁ de la première lentille demi-sphérique à liquide contrôlable électrostatiquement (10) et une seconde tension de commande (V₂) pour contrôler la longueur focale f₂ de la seconde lentille demi-sphérique à liquide contrôlable électrostatiquement (14), où une somme de la première tension de commande et de la seconde tension de commande (V₁ + V₂) est définie à une valeur constante prédéterminée déterminant la longueur focale d'ensemble (f) et la différence des tensions de commande (V₁ - V₂) détermine une longueur de chemin optique du collimateur / la différence de phase (ΔΦ).

7. Ensemble laser (40) selon la revendication 8, dans lequel :

le circuit de commande (41) délivre en sortie un premier signal de commande déterminant la longueur focale (f) du collimateur (23) et un second signal de commande (ΔU) déterminant la longueur de chemin optique / phase du collimateur, et où

le convertisseur de signal de commande (45) convertit les signaux de commande (U, ΔU) en la première tension de commande (V₁) et la seconde tension de commande (V₂).

8. Ensemble laser (40) pour un réseau de données optiques selon l'une quelconque des revendications 4 à 7, comprenant en outre :

une source de référence optique (42) conçue pour délivrer un signal optique de référence, un mélangeur optique (43) conçu pour mélanger le signal optique de référence et un signal de sortie du laser (20) et pour ainsi générer un signal de fréquence intermédiaire, et une source de référence locale conçue pour fournir une fréquence de référence locale, où l'unité de commande (41) du laser (20) est conçue pour comparer la fréquence intermédiaire à la fréquence de référence locale, de préférence une référence à quartz, et pour contrôler le collimateur (23) pour augmenter la phase lorsque la fréquence de sortie est supérieure à la fréquence de référence locale et pour diminuer la phase lorsque la fréquence de sortie est inférieure à la fréquence de référence locale.

9. Ensemble laser (40) selon la revendication 8, dans lequel le circuit de commande (41) est conçu pour déterminer une amplitude du signal de fréquence intermédiaire et pour contrôler la longueur focale du collimateur (23) de manière à ce que l'amplitude du signal de sortie du laser (20) atteigne un maximum.

10. Ensemble laser (40) selon l'une des revendications 8 ou 9, comprenant en outre :

une diode de surveillance (44) conçue pour délivrer un signal de retour comprenant des informations sur une amplitude d'un signal de sortie du laser (20), où le circuit de commande (41) est conçu pour contrôler la longueur focale du collimateur (23) de manière à ce que l'amplitude du signal de sortie du laser (20) atteigne un maximum.

11. Dispositif de transmission de données optiques, comprenant :

un récepteur hétérodyne et un ensemble laser (40) selon une des revendications 4 à 10, où la source de référence optique (42) est un signal d'entrée du récepteur hétérodyne.

12. Dispositif de transmission de données optiques, comprenant :

un récepteur hétérodyne et un ensemble laser (40) selon les revendications 8 à 10, où le mélangeur optique (43) est une photodiode destinée à recevoir un signal de données optiques du récepteur hétérodyne.

Drawing